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Introduction: The incidence of normal coronary arteries in patients referred for invasive coronary angiography (ICA) ranges from 30-60%. We sought to evaluate patterns of referral, assess the rate of appropriate catheterization and determine the prevalence of coronary artery disease (CAD) in our population by appropriateness and indication. Methods: Retrospective analysis was performed on 930 consecutive patients undergoing diagnostic ICA. Indications for ICA were reviewed and appropriate use criteria (AUC) were applied to the cohort retrospectively. Patients with known CAD, prior MI, CHF, or indication for pre-transplant workup or cardiac surgery were excluded. Rates of non-obstructive (21-49% stenosis) and obstructive CAD (≥50%) were compared by appropriateness status using Fisher’s Exact Testing. Results: Of the 930 patients studied, 55.6% were male with median age of 62 and 10-year ASCVD risk score of 17.7%. Acute coronary syndrome (ACS) was the most prevalent indication for referral (48.5%) with a 68.6% prevalence of obstructive CAD. A positive stress test was the indication in 18.9% with a 51.4% rate of obstructive CAD. The rates of the remaining referral indications are given in Figure 1. In those referred appropriately for angiography (n=923), the prevalence of obstructive disease was 55.9% (n=516), non-obstructive disease 13.6% (n=125), and normal coronaries 30.6%(n=282). Inappropriate referral was identified in only 7 patients (0.8%), all of whom had normal coronaries with p Conclusions: At a single quaternary care academic center the majority of coronary angiographies performed invasively are appropriate by AUC. Despite adherence to AUC, there continues to be a large number of patients with no evidence of obstructive disease, including in those with ACS. Further research is needed to further refine the AUC and its role in risk stratification for obstructive CAD.

Introduction: Current cardiac magnetic resonance (CMR) T1 mapping techniques such as Modified Look-Locker inversion recovery (MOLLI) imaging have limited resolution, but the Accelerated and Navigator-Gated Look-Locker Imaging for Cardiac T1 Estimation (ANGIE) is a novel CMR sequence with spatial resolution suitable for T1 mapping of the thin-walled RV. Hypothesis: In pulmonary hypertension (PH) and heart failure (HF), RV extracellular volume (ECV) fraction (as a surrogate measure for RV fibrosis) is a unique parameter describing RV structure that tends to increase with increasing RV size and declining RV function. Methods: Patients with either World Health Organization group 1 or group 4 pulmonary hypertension (PH) or heart failure with reduced ejection fraction (HFrEF) were recruited to undergo contrast-enhanced CMR. RV and LV ECV fractions were determined using pre-contrast and post-contrast T1 mapping using ANGIE (RV and LV) and MOLLI (LV). Results: 22 patients (41% female, median age 61 years old, IQR 51-70 years old) were enrolled, including n=12 with PH and n=10 with HFrEF. ANGIE ECV imaging was of high quality (Figure). A multivariable linear model with RVEF and RVEDVI as independent variables and RVECV as the outcome variable showed independent associations for RVEF and RVEDVI with RVECV (R 2 =0.553) (Table), consistent with a complex relationship involving RV function, dilation, and fibrosis. Conclusions: Pre- and post-contrast ANGIE imaging provides high-resolution ECV determination for the thin-walled RV. RV fibrosis increases with increasing RV size and decreasing overall RV function. Further studies of RVECV in PH and HFrEF are indicated.